1. Field of the Invention
The invention relates to a technique for the handover of packet-switched data flows, particularly between systems supporting different radio access technologies and/or different modes of operation.
2. Description of the Related Art
The deployment of new radio technologies is typically, at least initially, in geographically limited areas. To meet user coverage needs, it is desirable to provide for a handover to an existing or alternative radio technology when a user moves out of an area supported by new but geographically limited radio technology.
An example is the deployment of the UMTS radio access network (UTRAN), which offers limited geogpraphical coverage, at least initially, in comparison to the more established GSM EDGE radio access network (GERAN). It is proposed, in TSG GERAN, to provide for inter-radio access technology (inter-RAT) packet switched (PS) handover to address this issue. Specifically, it is proposed to provide for a handover between a GERAN A/Gb mode of operation and a UTRAN/CDMA2000 mode of operation.
Within any given radio access technology, there may also be different operational modes. For example, within GERAN there is an A/Gb mode and an Iu mode. TSG GERAN further specifies an inter-mode packet switched (PS) handover between the A/Gb mode and the Iu mode.
In GERAN A/Gb mode a base station subsystem packet flow context (BSS PFC), identified by a packet flow identifier (PFI), may be subject to packet switched (PS) handover. The mobile station (MS) to which this PFC is assigned is therefore also subject to handover.
In GERAN Iu mode and UTRAN a radio access bearer (RAB) identified by a RAB identifier may be subject to relocation, and the user equipment (UE) to which the RAB identifier is assigned is also relocated.
Hereafter, UTRAN mode and GERAN Iu mode are referred to as Iu mode, while A/Gb mode refers to GERAN A/Gb mode.
There is a need to support inter-mode and inter-RAT PS handover and hence seamless interruption of data flows during handover.
Packet switched handover in GERAN A/Gb mode is not yet defined. 3GPP TSG GERAN is currently specifying the packet switched handover in GERAN A/Gb mode. The signaling solution to supporting inter-mode and inter-RAT packet switched handover is presented in TS 43.129 (Stage 2 draft for PS handover in A/Gb mode).